434
FXUS65 KBOU 141733
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1133 AM MDT Sun Jul 14 2024

.KEY MESSAGES...

- Heat wave and Heat Advisory continues today with highs reaching
  100 to 105 degrees across the Urban Corridor. Across the plains
  highs may stay in the upper 90`s to around 100.  Important to
  take steps to limit outdoor activity, find ways to cool off, and
  stay hydrated as much as possible.

- Dry lightning threat and new fire starts possible today.

- Strong and gusty microburst winds possible bothy today and
  Monday with scattered high based showers and isolated
  thunderstorms.

- Only slight heat relief expected Monday, with far more relief
  by Tuesday. Increasing chance of showers and thunderstorms
  both Tuesday and Wednesday.

- More typical summer weather for the latter half of this week
  with scattered afternoon showers and storms, and temperatures
  averaging closer to normal.

&&

.UPDATE...
Issued at 942 AM MDT Sun Jul 14 2024

An outflow boundary is moving across the northeast plains this
morning and currently is along a New Raymer to Fort Morgan to
Woodrow line.  Behind this boundary temps are mainly in the 70`s
while west of it readings are in the 85-90 degree range.  Main
question is will it move into the I-25 Corridor or washout.  If it
washes out then previous fcst highs along the I-25 Corridor should
be reached.  Behind this boundary readings may hold in the 90`s this
aftn and not get above 100 degrees.  Will continue to monitor trends
over the next 1-2 hours and make temperature adjustments if needed.

Meanwhile, there is more more moisture over the area today than
yesterday so still expect better coverage of mainly higher based
showers and storms.  There still is some question as to how much
lightning there will be over the higher terrain as activty may end
up being more higher based showers than storms.  Across the plains,
behind the outflow boundary there is better low level moisture. Thus
this will lead to better instability along with some potential for
stronger tstm activity by late aftn into the early evening hours.
Meanwhile, to the west of the boundary there will be larger T-TD
spreads with a higher potential for microburst activity.

&&

.SHORT TERM /Through Monday/...
Issued at 228 AM MDT Sun Jul 14 2024

Day three of the Colorado heat wave will continue today as
temperatures are expected to range from the upper 90s to 104
across the plains and urban corridor. Once again, a Heat Advisory
will be in place from 10 AM to 8 PM for the aforementioned
locations. With persistent dry conditions and potential for dry
lightning across the higher terrain this afternoon, critical fire
weather conditions will be a concern for today, therefore we have
upgraded our Fire Weather Watch to a Red Flag Warning from 12 PM
this afternoon through 9 PM this evening. See the Fire Weather
section below for more details.

The general pattern remains consistent with what has been discussed
over the last week with heat headlines. Anomalous 500 mb heights
(~5970 m) mixed with elevated 700 mb temperatures (~20C) will
translate to surface temperatures reaching for the record books. The
latest guidance shows a slight decrease in 700 mb temperatures from
previous model runs (only by about 1-2C), and with increased cloud
coverage expected for today, temperatures may be slightly cooler
than previously expected. It will still be HOT...just maybe
slightly less HOT. The forecast high temp for DIA is 101F, which
is still a degree hotter than the daily record for this location
(last observed in 1878). While we know today will be hot, there is
some uncertainty regarding whether forecast temperatures across
portions of the plains for today will come to fruition as current
radar shows an MCS now entering northern Nebraska. This could
bring a surge of northeasterly winds to the forecast area later
this morning as it dissipates. With a similar occurrence
yesterday morning aiding in temperatures being slightly lower than
expected, we will monitor conditions this morning and adjust
temperatures down if needed. More certainty resides in the high
mountain valleys reaching the high 80s with mid 70s across the
other higher terrain. With flow aloft transitioning to a more
westerly flow later today, overnight temperatures along the base
of the foothills may stay elevated slightly more than other
locations due to compressional heating effects. Across the plains,
mid to high 60s are expected, and mid to high 40s for the higher
elevations.

Forecast soundings indicate an environment capable of producing high-
based convection and potential for gusty outflows with DCAPE values
ranging from 1200-1900 J/kg throughout the afternoon. Instability
still looks marginal, however, slightly higher than yesterday. CAMs
show a greater coverage of showers than yesterday, and current
satellite imagery shows increased mid-level moisture as well.
Therefore, we are expecting scattered showers and isolated weak
thunderstorms to develop this afternoon across the mountains and
move eastward onto the plains through the evening. These will likely
contain isolated dry lightning as well. These showers will be
capable of producing light rainfall and gusty microburst winds to
50 mph or greater. For those of you considering recreating on the
water, it would be a good day to be aware that gusty winds can
occur suddenly in this environment and create dangerous
conditions.

&&

.LONG TERM /Monday night through Saturday/...
Issued at 330 AM MDT Sun Jul 14 2024

While it will still be hot on Monday with a quick warmup and
shallow inversions to start the day, we will see a little heat
relief in the form of a weak backdoor "cool" front. This front
appears to push across the plains in the morning but given the
shallow inversions and expected strong mixing, the front or push
will essentially lose its identity. That said, the turn to
upslope winds and increasing mid/upper level moisture and
cloudiness will serve to take a few degrees of today`s scorching
heat. Mid to upper 90s should generally be the highs across the
plains and I-25 Corridor. Shower and storm coverage should see an
uptick with the increase in mid/upper level moisture as well as
the upslope component and weak low level moisture advection.
However, significant DCAPE near 1500-1800 J/kg still means strong,
gusty outflow winds from any convective activity.

Real relief from the heat will occur for Tuesday, as a reinforcing
cold front pushes across the plains. This will also bring
additional low level moisture, resulting in an increase in shower
and storm coverage and propensity for more rainfall from storms
for a change as storm intensity picks up. That uptick in
convection should continue into Wednesday, along with cooler
temperatures (80-90% chance of temperatures below normal across
the plains for Wednesday). The deterministic forecast rides close
to ensemble average of mid 80s across the plains.

For Thursday through Saturday, there is reasonable agreement that
the ridge retrogrades westward into the Desert Southwest and Great
Basin, while a trough settles across the Great Lakes and Midwest.
We`ll be on the edge of the more significant cooling in this
northerly flow pattern, and hard to gauge when fronts with
additional cooling could move through. Right now, the
deterministic forecast is close to climatology with regard to
temperatures and PoPs which seems fine, but one or two of those
days will likely end up on the cooler side of guidance depending
on timing of backdoor cold fronts.

&&

.AVIATION /18Z TAFS through 18Z Monday/...
Issued at 1128 AM MDT Sun Jul 14 2024

Winds will trend to more northerly 19z.  Still expect sct high
based showers to move across by 21z with mainly virga and brief
gusty winds from 40 to 50 mph thru 01z. There could be some
additional high based showers between 01z and 03z but wind speeds
should be lower. Wind directions will be quite chaotic due
to outflow from the showers but will keep them north thru 01z
with a gradually shift to SSW by 03z. Winds may go more WSW after
08z.

&&

.FIRE WEATHER...
Issued at 330 AM MDT Sun Jul 14 2024

Widespread elevated to near-critical fire weather conditions will
remain in place across most of the area on Sunday and hot and dry
conditions prevail. Additionally, isolated to scattered dry
lightning will result in a heightened threat for lightning-induced
wildfire ignitions, particularly in the mountains, foothills, and
northern urban corridor. Thus, we`ve upgraded the Fire Weather
Watch to a Red Flag Warning for these locations.

Monday could continue a dry lightning threat with still dry and
very warm low levels. However, overall moisture content in the
atmosphere is increasing so most storms, at least in the
mountains, should be producing at least some rainfall.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM MDT this evening for COZ211>218-238.

Heat Advisory until 8 PM MDT this evening for COZ038>051.

&&

$$

UPDATE...RPK
SHORT TERM...Bonner
LONG TERM...Barjenbruch
AVIATION...RPK
FIRE WEATHER...Bonner